Department of Ophthalmology and Ross Eye Institute, University at Buffalo, State University of New York, Buffalo, New York, United States.
Center for Computational Research, New York State Center of Excellence in Bioinformatics and Life Sciences, State University of New York, Buffalo, New York, United States.
Invest Ophthalmol Vis Sci. 2023 Nov 1;64(14):40. doi: 10.1167/iovs.64.14.40.
Diabetic retinopathy (DR) is a leading cause of blindness in working-age adults characterized by retinal dysfunction and neurovascular degeneration. We previously reported that deletion of X-box binding protein 1 (XBP1) leads to accelerated retinal neurodegeneration in diabetes; however, the mechanisms remain elusive. The goal of this study is to determine the role of XBP1 in the regulation of photoreceptor synaptic integrity in early DR.
Diabetes was induced by streptozotocin in retina-specific XBP1 conditional knockout (cKO) or wild-type (WT) mice to generate diabetic cKO (cKO/DM) or WT/DM mice for comparison with nondiabetic cKO (cKO/NDM) and WT/NDM mice. Retinal morphology, structure, and function were assessed by immunohistochemistry, optical coherence tomography, and electroretinogram (ERG) after 3 months of diabetes. The synapses between photoreceptors and bipolar cells were examined by confocal microscopy, and synaptic integrity was quantified using the QUANTOS algorithm.
We found a thinning of the outer nuclear layer and a decline in the b-wave amplitude in dark- and light-adapted ERG in cKO/DM mice compared to all other groups. In line with these changes, cKO mice showed increased loss of synaptic integrity compared to WT mice, regardless of diabetes status. In searching for candidate molecules responsible for the loss of photoreceptor synaptic integrity in diabetic and XBP1-deficient retinas, we found decreased mRNA and protein levels of DLG4/PSD-95 in cKO/DM retina compared to WT/DM.
These findings suggest that XBP1 is a crucial regulator in maintaining synaptic integrity and retinal function, possibly through regulation of synaptic scaffold proteins.
糖尿病视网膜病变（DR）是导致工作年龄成年人失明的主要原因，其特征是视网膜功能障碍和神经血管退化。我们之前报道过，X 盒结合蛋白 1（XBP1）缺失会导致糖尿病中视网膜神经退行性变加速；然而，其机制仍不清楚。本研究的目的是确定 XBP1 在调节早期 DR 中光感受器突触完整性中的作用。
通过链脲佐菌素在视网膜特异性 XBP1 条件性敲除（cKO）或野生型（WT）小鼠中诱导糖尿病，以生成糖尿病 cKO（cKO/DM）或 WT/DM 小鼠，与非糖尿病 cKO（cKO/NDM）和 WT/NDM 小鼠进行比较。通过免疫组织化学、光学相干断层扫描和视网膜电图（ERG）在糖尿病 3 个月后评估视网膜形态、结构和功能。通过共聚焦显微镜检查光感受器和双极细胞之间的突触，并使用 QUANTOS 算法量化突触完整性。
我们发现 cKO/DM 小鼠与其他所有组相比，外核层变薄，暗适应和明适应 ERG 的 b 波振幅下降。与这些变化一致，cKO 小鼠的突触完整性丧失比 WT 小鼠增加，无论糖尿病状态如何。在寻找导致糖尿病和 XBP1 缺失视网膜中光感受器突触完整性丧失的候选分子时，我们发现 cKO/DM 视网膜中的 DLG4/PSD-95 mRNA 和蛋白水平较 WT/DM 降低。
这些发现表明 XBP1 是维持突触完整性和视网膜功能的关键调节剂，可能通过调节突触支架蛋白。
